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Sunday, 14 November 2010

Rainforest Grasshoppers

There are only a few grasshopper species that could be considered as true rainforest inhabitants in northern Australia. Reasons for this are unclear. The normally dominant family, the Acrididae, contributes only a single species in the Daintree, Atherton Tablelands and Kuranda rainforests. Howwever, there are plenty of acridid species that occupy disturbed areas adjacent to rainforests. These are not dependent on the rainforest habitat but are tropical species that are at home amongst weeds and other plants typical of disturbed or "open" situations.

Surprisingly, the dominant family in the rainforests in northeastern Australia is the Tetrigidae, the Pygmy Grasshoppers. This family is the poorest known of Australian grasshoppers. Reasons for this are many but at present, no one is studying this family in Australia.

The Eumastacidae, Pyrgomorphidae and the Acrididae each contribute a single species that can be considered as part of the rainforest fauna. The inclusion of the acridid species is a bit marginal as it lives in clearings, feeding on graasses that appear after an opening caused by a tree-fall, landslide or some other disaster. Unlike the other acridid species noted above, these grasshoppers do not stray far from the rainforest.

This is a very typical Pygmy Grasshopper (Tetrigidae: Tetriginae), probably the genus Paratettix. The family is easily recognised by the elongated pronotum (the fore part of the thorax just behind the head) that extends, spine-like well beyond the tip of the abdomen. If the species is winged (and some species may be winged or not!) the forewings (tegmina) are represented as minute, ovoid pads. (see red arrow below)

Tetrigid species are notoriously difficult to identify because each species exhibits considerable individual variation. Often you can find several species at a given habitats and there may be forms dimorphic for wing presence, pronotal length etc all occurring together.

Australian tetrigids are commonly found along watercourses. They also live in gravel along paths and are frequently found on wet lawns. Many feed on algae and diatoms.

This is another tetrgid, genus Loxilobus (subfamiliy Scelimeninae). This genus seems characterised by the downwards projecting spine-like appendage that is seen between the fore and middle legs. Although this greenish colour seems distinctive, there is great variation in this and other tetrigids and colour alone is not a reliable character to disitnguish the species.This is a little gem of a tetrigid. It is smaller than most, wingless and characterised by the hood-like projection of the pronotum that extends over the head. This may be an undescribed genus--but one must be careful, there may be a related species in New Guinea that has a generic name. This species lives on bark at the base of large rainforest trees. It may feed on moss.If it's the bizarre that interests you, here is a rainforest tetrigid from the Muller Range in Papua New Guinea. This is a common species where it occurs and is active by day feeding on mosses that grow on leaf surfaces. We don't know its identity. It possesses a combination of bizarre characters, the most obvious of which is the elongated head. There is no similar species in Australia.

The Pyrgomorphidae contributes a single genus and species to the Kuranda rainforest. Desmopteratruncatipennis Sjøstedt, The Large Rainforest Pyrgomorph, occupies a narrow range along the coast from the Daintree to the Atherton Tablelands. Its specific name is derived from the truncated or cut-off appearance of the wings. To the north in the rainforests of the Cape, the smaller Desmopterella sp. can be found.The Large Rainforest Pyrgomorph, male brown morph. This species has a variety of colour forms and, interestingly, none include shades of green.

The Large Rainforest Pyrgomorph, male, mottled brown and white morph.

D.truncatipennis, The Large Rainforest Pyrgomorph, is easily recognised by its large size and conical head.

Nymphs present an unusual appearance with a series of ridges running along the middle of the dorsal part of the insect. This grasshopper inadvertently avoids the depredations of the Cane Toad, Bufomarinus, by its normal nocturnal activity. After dark the grasshoppers ascend shrubs and small trees to feed on green leaves. They are, therefore, out of the reach of the cane toads that search the ground for food. During the day, the grasshoppers live in dry leaf litter, sometimes in close proximity to the toads, but the toads are inactive during the day and the grasshoppers are of no interest.

Biroella sp., adult female

The Eumastacidae are a primarily tropical group occurring worldwide. The notable exception within Australia is the endemic subfamily Morabinae. These Matchstick grasshoppers can be found in almost all terrestrial habitats with the exception of the tropical rainforest. However, there is a eumastacid example in tropical rainforests in the form of the genus Biroella. These grasshoppers are poorly collected because they sit on foliage often high in the trees out of reach of entomologists. Many species, like the one shown here, have very short forewings. Collectors often discard them thinking they are immature and not identifiable. The best way of sampling for these species is with canopy fogging techniques.

Methiolapicta Sjøstedt, the Red-legged Methiola, is the only acridid grasshopper you are likely to encounter in the rainforest proper. It is common in the Daintree, Kuranda and Atherton Tablelands. As noted above, it is a grass feeder.

Additional information about Australia Grasshoppers can be found in this guide which is available over the web at Andrew Isles Books.

3 comments:

David, the PNG tetrigid is Ophiotettix sp. (Metrodorinae), as identified by Josef Tumbrinck, who has an online checklist of New Guinea tetrigids:http://www.papua-insects.nl/insect%20orders/Orthoptera/Tetrigidae/Tetrigidae.htm

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About Me

David and family moved to Kuranda, Queensland in 2002, following retirement from CSIRO Canberra, Australia. David, Barbara and an assortment of wildlife live in a rainforest setting. It is their first experience living in the tropics.
David's major interest is Entomology. He continues research in the Orthopteroid insects and is keenly interested in the biology of the rainforest.
This blog is a narrative of observations made in and around Kuranda.
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